1. Field of Disclosed Subject Matter
This disclosure relates to systems and methods for providing improved single pass cleaning of ink residue and other residual products from a reimageable surface on an imaging member in a proposed variable data digital lithographic image forming architecture.
2. Related Art
U.S. Patent Application Publication No. 2012/0103212 A1 (the 212 Publication) published May 3, 2012 and based on U.S. patent application Ser. No. 13/095,714, which is commonly assigned and the disclosure of which is incorporated by reference herein in its entirety, proposes systems and methods for providing variable data lithographic and offset lithographic printing or image receiving medium marking in image forming system. The systems and methods disclosed in the 212 Publication are directed to improvements on various aspects of previously-attempted variable data imaging lithographic marking concepts to achieve effective truly variable digital data lithographic printing.
According to the 212 Publication, a reimageable surface is provided on an imaging member, which may be a drum, plate, belt or the like. The reimageable surface may be composed of, for example, a class of materials commonly referred to as silicones, including polydimethylsiloxane (PDMS) among others. The reimageable surface may be formed of a relatively thin layer over a mounting layer, a thickness of the relatively thin layer being selected to balance printing or marking performance, durability and manufacturability.
The 212 Publication describes, in requisite detail, an exemplary variable data lithography system 100 such as that shown, for example, in FIG. 1. A general description of the exemplary system 100 shown in FIG. 1 is provided here. Additional details regarding individual components and/or subsystems shown in the exemplary system 100 of FIG. 1 may be found in the 212 Publication.
As shown in FIG. 1, the exemplary system 100 may include an imaging member 110. The imaging member 110 in the embodiment shown in FIG. 1 is a drum, but this exemplary depiction should not be read in a manner that precludes the imaging member 110 being a plate or a belt, or of another known configuration. The imaging member 110 is used to apply an inked image to an image receiving media substrate 114 at a transfer nip 112. The transfer nip 112 is produced by an impression roller 118, as part of an image transfer mechanism 160, exerting pressure in the direction of the imaging member 110. The exemplary system 100 may be used for producing images on a wide variety of image receiving media substrates 114. The 212 Publication also explains the wide latitude of marking (printing) materials that may be used, including marking materials with pigment densities greater than 10% by weight. As does the 212 Publication, this disclosure will use the term ink to refer to a broad range of printing or marking materials to include those which are commonly understood to be inks, pigments, and other materials which may be applied by the exemplary system 100 to produce an output image on the image receiving media substrate 114.
The 212 Publication depicts and describes details of the imaging member 110 including the imaging member 110 being comprised of a reimageable surface layer formed over a structural mounting layer that may be, for example, a cylindrical core, or one or more structural layers over a cylindrical core.
The exemplary system 100 includes a dampening solution subsystem 120 generally comprising a series of rollers, which may be considered as dampening rollers or a dampening unit, for uniformly wetting the reimageable surface of the imaging member 110 with dampening solution. A purpose of the dampening solution subsystem 120 is to deliver a layer of dampening solution, generally having a uniform and controlled thickness, to the reimageable surface of the imaging member 110.
Once the dampening solution is metered onto the reimageable surface of the imaging member 110, a thickness of the dampening solution may be measured using a sensor 125 that may provide feedback to control the metering of the dampening solution onto the reimageable surface of the imaging member 110 by the dampening solution subsystem 120.
Once a precise and uniform amount of dampening solution is provided by the dampening solution subsystem 120 on the reimageable surface of the imaging member 110, and optical patterning subsystem 130 may be used to selectively form a latent image in the uniform dampening solution layer by image-wise patterning the dampening solution layer using, for example, laser energy. The reimageable surface of the imaging member 110 should ideally absorb most of the laser energy emitted from the optical patterning subsystem 130 close to the surface to minimize energy wasted in heating the dampening solution and to minimize lateral spreading of heat in order to maintain a high spatial resolution capability. While the optical patterning subsystem 130 is described above as being a laser emitter, it should be understood that a variety of different systems may be used to deliver the optical energy to pattern the dampening solution.
The mechanics at work in the patterning process undertaken by the optical patterning subsystem 130 of the exemplary system 100 are described in detail with reference to FIG. 5 in the 212 Publication. Briefly, the application of optical patterning energy from the optical patterning subsystem 130 results in selective evaporation of portions of the layer of dampening solution.
Following patterning of the dampening solution layer by the optical patterning subsystem 130, the patterned layer over the reimageable surface of the imaging member 110 is presented to an inker subsystem 140. The inker subsystem 140 is used to apply a uniform layer of ink over the layer of dampening solution and the reimageable surface layer of the imaging member 110. The inker subsystem 140 may use an anilox roller to meter an ink onto one or more ink forming rollers that are in contact with the reimageable surface layer of the imaging member 110. Separately, the inker subsystem 140 may include other traditional elements such as a series of metering rollers to provide a precise feed rate of ink to the reimageable surface. The inker subsystem 140 may deposit the ink to the pockets representing the imaged portions of the reimageable surface, while ink deposited on the unformatted portions of the dampening solution will not adhere based on the hydrophobic and/or oleophobic nature of those portions.
The cohesiveness and viscosity of the ink residing in the reimageable layer of the imaging member 110 may be modified by a number of mechanisms. One such mechanism may involve the use of a rheology (complex viscoelastic modulus) control subsystem 150. The rheology control system 150 may form a partial crosslinking core of the ink on the reimageable surface to, for example, increase ink cohesive strength relative to the reimageable surface layer. Curing mechanisms may include optical or photo curing, heat curing, drying, or various forms of chemical curing. Cooling may be used to modify rheology as well via multiple physical cooling mechanisms, as well as via chemical cooling.
The ink is then transferred from the reimageable surface of the imaging member 110 to a substrate of image receiving medium 114 using a transfer subsystem 160. The transfer occurs as the substrate 114 is passed through a transfer nip 112 between the imaging member 110 and an impression roller 118 such that the ink within the voids of the reimageable surface of the imaging member 110 is brought into physical contact with the substrate 114. With the adhesion of the ink having been modified by the rheology control system 150, modified adhesion of the ink causes the ink to adhere to the substrate 114 and to separate from the reimageable surface of the imaging member 110. Careful control of the temperature and pressure conditions at the transfer nip 112 may allow transfer efficiencies for the ink from the reimageable surface of the imaging member 110 to the substrate 114 to exceed 95%. While it is possible that some dampening solution may also wet substrate 114, the volume of such a dampening solution will be minimal, and will rapidly evaporate or be absorbed by the substrate 114.
In certain offset lithographic systems, it should be recognized that an offset roller, not shown in FIG. 1, may first receive the ink image pattern and then transfer the ink image pattern to a substrate according to a known indirect transfer method using an offset roller or other device as an intermediate transfer body.
Following the transfer of the majority (95+%) of the ink to the substrate 114 at the transfer nip 112, any residual ink and/or residual dampening solution must be removed from the reimageable surface of the imaging member 110 to prepare the reimageable surface to repeat the digital image forming operation without “ghosting.” This removal is most preferably undertaken without scraping or wearing the reimageable surface of the imaging member 110. An air knife or other like non-contact device may be employed to remove residual products. It is anticipated, however, that some amount of ink residue may remain. Removal of such remaining ink residue may be accomplished through use of some form of active cleaning subsystem 170. The 212 Publication describes details of such a cleaning subsystem 170 including at least a first cleaning member such as a sticky or tacky member in physical contact with the reimageable surface of the imaging member 110, the sticky or tacky member removing residual ink and any remaining small amounts of surfactant compounds from the dampening solution of the reimageable surface of the imaging member 110. The sticky or tacky member may then be brought into contact with a smooth roller to which residual ink may be transferred from the sticky or tacky member, the ink being subsequently stripped from the smooth roller by, for example, a doctor blade or other like device and collected as waste.
The 212 Publication details other mechanisms by which cleaning of the reimageable surface of the imaging member 110 may be facilitated. Regardless of the cleaning mechanism, however, cleaning of the residual ink and dampening solution from the reimageable surface of the imaging member 110 is essential to preventing ghosting in subsequent image forming operations as the images change. Once cleaned, the reimageable surface of the imaging member 110 is again presented to the dampening solution subsystem 120 by which a fresh layer of dampening solution is supplied to the reimageable surface of the imaging member 110, and the process is repeated.